The present invention relates to a method for tipping a load by a working machine and a tipping device adapted for a working machine. The method and device is suitable for heavy vehicles, such as trucks and construction vehicles.
Heavy vehicles, especially trucks, articulated haulers and other construction equipment vehicles are often provided with a tipping device adapted to unload goods transported by the load carrier of the vehicle. Such a load carrier may be e.g. a platform for carrying sand, stones etc., a concrete mixer, a concrete hopper or a vessel for carrying dry, powdery products such as flour, grain etc. The goods are unloaded by tipping the load carrier by one or more load cylinders. The pressure to the load cylinders is provided by a hydraulic oil pressure system on the vehicle. In order to avoid overloading the hydraulic system, a maximal tipping pressure is predefined by the control unit of the hydraulic system. This ensures that the vehicle and thus the tipping device is not overloaded.
This maximal tipping pressure normally has an allowed additional positive pressure such that a somewhat higher tipping pressure than the nominal tipping pressure is allowed. This additional pressure is provided in order to ensure that the nominal load can always be unloaded, regardless of other parameters influencing the load pressure. Such parameters may be e.g. the temperature of the hydraulic oil, the distribution of the load on the load carrier, the altitude of the vehicle and irregularities of the ground. In this way, the driver of the vehicle can be sure that he will always be able to unload. However, the operator may also use this additional pressure margin on a regular basis, constantly overloading the vehicle. This will cause excessive wear of the hydraulic system and the vehicle which may lead to unnecessary repairs of the vehicle and may also cause incorrect warranty demands.
Different solutions to this problem are known. One way is to minimize the allowed additional pressure margin such that only the nominal load can be tipped, regardless of the outer circumstances. Another way is to monitor and save tipping parameters exceeding predefined values in order to be able to determine if an excessive load has been used. This will however not prevent the overload.
There is thus a need for an improved tipping method and an improved tipping device.
It is desirable to provide an improved method for tipping a load by a working machine. It is also desirable to provide an improved tipping device for a working machine.
In a method for tipping a load by a working machine according to an aspect of the invention, where the working machine comprises a load carrier and at least one lift cylinder adapted to raise the load carrier for tipping the load, the steps of obtaining a measure for the inclination angle of the working machine, where the inclination of the working machine is such that the rear end of the working machine is higher than the front end thereof, allowing a first maximal tipping pressure to the lift cylinder for raising the load carrier when the inclination angle is less than a predefined inclination angle, and allowing a second maximal tipping pressure to the lift cylinder for raising the load carrier when the inclination angle is greater than the predefined inclination angle, where the second maximal tipping pressure exceeds the first maximal tipping pressure are comprised.
By this first embodiment of the method for tipping a load by a working machine according to an aspect of the invention, a method where the inclination angle of the working machine is used to control the tipping pressure is provided. The tipping pressure can thus be set to a first tipping pressure value when the inclination angle of the working machine is less than a predefined inclination value, and to a second tipping pressure value when the inclination angle of the vehicle exceeds the predefined inclination value. The predefined inclination angle value may be pre-set by the manufacturer or may be set depending on the use of the working machine or may be set depending on the marked. The predefined inclination angle is preferably such that the first tipping pressure value is used when the working machine is substantially horizontal and when the inclination of the working machine is relatively small. In one example, the predefined inclination angle is less than eight degrees, and preferably less than four degrees.
In an advantageous development of the inventive method, the second maximal tipping pressure is a function of the inclination angle. In this way, the tipping pressure can be adapted to the actual inclination of the working machine. In this way, a temporary high tipping pressure can be allowed which is adapted to the actual tipping conditions. The second tipping pressure can also be limited by a third, maximal tipping pressure value which corresponds to the maximal allowed pressure of the hydraulic system or the working machine. This will secure that the tipping pressure of the working machine never exceeds a value where the hydraulic system will break down or where parts will be damaged or cause hazardous situations due to temporary overload.
The inclination angle is either measured directly with an electronic inclination sensor or an inclinometer, or may be estimated by measuring the load distribution of the load. The load distribution may be measured either by measuring the load on the front axle and the rear axle, axles or bogie by using axle load sensors or by measuring the load at the front and at the rear of the load carrier by using load sensors mounted on the load carrier. The measured load values are compared with stored values regarding the nominal load distribution for the work machine. In this way, the actual load distribution can give an estimation of the inclination angle for the work machine.
In an advantageous development of the inventive method, the second tipping pressure is displayed on a display in the working machine. Preferably, the display is positioned in the instrument cluster and may be integrated in the instrument cluster and may be pan of the regular driver information system of the working machine. By showing the actual second pressure to the driver, the driver will see the available tipping pressure and may, by experience, assess if the available tipping pressure will suffice for the tipping to be done. The second tipping pressure may also be stored in a memory comprising a table such that the used tipping pressures can be monitored at a later stage. The tipping pressure may also be stored together with the inclination angle.
In a tipping device for a working machine, the working machine comprising a load carrier and at least one lift cylinder adapted to raise the load carrier, the object of the invention is achieved in that the tipping device comprises a means for adjusting the maximal allowed tipping pressure to the lift cylinder based on the inclination of the working machine.
By this first embodiment of the inventive tipping device, the tipping pressure of the tipping device is adapted to the inclination of the working machine. In this way, it is possible to control the tipping pressure of the working machine such that a constant overload of the tipping device is avoided, due to an allowed additional pressure to the tipping pressure. By controlling the tipping pressure in dependence of the inclination angle of the working machine, it can be ensured that the tipping device and thus the working machine is not overloaded.
In an advantageous development of the tipping device, the tipping device is adapted to operate with a first maximal tipping pressure when the inclination angle is less than a predefined inclination angle, and with a second maximal tipping pressure when the inclination angle is greater than the predefined inclination angle, and where the second maximal tipping pressure exceeds the first maximal tipping pressure. In this way, the tipping pressure can be controlled in dependency of the inclination angle of the working machine.
In an advantageous development of the inventive tipping device, the tipping pressure is a function of the inclination angle of the working machine. In this way, the tipping pressure can be controlled in a more precise way.
In an advantageous development of the inventive tipping device, the tipping pressure is limited to a third, maximal allowed tipping pressure, which corresponds to the maximal allowed tipping pressure of the hydraulic system. In this way, it is ensured that the hydraulic system or the working machine is not overloaded, regardless of the inclination angle of the working machine.
In an advantageous development of the inventive tipping device, the means for adjusting the tipping pressure comprises an inclinometer connected to a variable pressure valve with a lever, such that the variable pressure valve adjusts the tipping pressure in dependency of the inclinometer. In this way, the tipping pressure can be controlled in dependency of the inclination of the working machine in an easy and reliable way.
In an advantageous development of the inventive tipping device, the means for adjusting the tipping pressure comprises an electronic inclination sensor that inputs the inclination angle to a control unit. The control unit adjusts the tipping pressure in dependency of the measured inclination signal by sending a signal to an electric variable pressure valve. In this way, the tipping pressure can be controlled in a more refined way.
In an advantageous development of the inventive tipping device, the means for adjusting the tipping pressure comprises load sensing means arranged on a front axle and a rear axle, axles or bogie of the work machine. The load sensing means are used to measure the load distribution between the front and the rear of the work machine. Since the nominal load distribution for the work machine is known and is stored in a memory, a deviation in the load distribution can be used to estimate an inclination angle of the work machine. The control unit adjusts the tipping pressure in dependency of the estimated inclination angle by sending a signal to an electric variable pressure valve. In this way, the tipping pressure can be controlled in a more refined way.
The inclination angle can also be estimated by measuring the load distribution of the load in the load carrier. The load distribution is measured by measuring the load at the front and at the rear of the load carrier by using load sensors mounted on the load carrier. The measured load values are compared with stored values regarding the nominal load distribution for the load carrier. In this way, the actual load distribution can give an estimation of the inclination angle for the work machine.